Here is a recently completed composition created entirely in Photoshop with no photographs. This was created after studying the book, 100% Photoshop. It teaches techniques to essentially paint in Photoshop, instead of requiring photographs for creating objects. These techniques are great building blocks for all photo editing.
Creating art in Photoshop has been quite an enlightening experience. Being able to digitally brush and simply undo things easily, and work in layers allows for much greater experimentation and perfection of an idea.
At least 30 hours involved in this creation but well worth the result!